Publisher Summary The vibrational spectrum of a molecule is determined by its three-dimensional structure and its vibrational force field. An analysis of this (usually infrared (IR) and Raman) spectrum can therefore provide information on the structure and on intramolecular and intermolecular interactions. The more probing the analysis, the more detailed is the information that can be obtained. Detailed analyses of the vibrational spectra of macromolecules, however, have provided a deeper understanding of structure and interactions in these systems. An important advance in this direction for proteins came with the determination of the normal modes of vibration of the peptide group in N-methylacetamide, and the characterization of several specific amide vibrations in polypeptide systems. Extensive use has been made of spectra-structure correlations based on some of these amide modes, including attempts to determine secondary structure composition in proteins. Polypeptide molecules exhibit many more vibrational frequencies than the amide modes. Over the years, some normal-mode calculations have provided greater insight into the spectra of particular molecules. However, these have often been based on approximate structures or have employed limited force fields. These force fields can now serve as a basis for detailed analyses of spectral and structural questions in other polypeptide molecules. The aim of this chapter is to present these recent developments in the vibrational spectroscopy of peptides, polypeptides, and proteins.

Vibrational spectroscopy and conformation of peptides, polypeptides, and proteins.

Cyclodextrins are extremely attractive components of artificial enzymes and other biomimetic materials. They are readily available, they bind hydrophobic substrates into their cavities in water solution, and they have two rims of hydroxyl groups (Figure 1) that can either react with substrates themselves or be used to attach other catalytic and functional groups. Of course, they have disadvantages. For one, unless they are extensively modified their complexes with substrates can be rather flexible and, perhaps, with unpredictable preferred geometry. They are also unstable to strong acid. Thus for some purposes such synthetic cavity species as calixerenes1 or synthetic macrocycles2-4 may have advantages. However, one of the chief advantages of cyclodextrins is highly attractivesthey are readily available, so it is possible to avoid the synthesis of a binding group and go directly to studies of what can be achieved with their use. Afterward, the lessons learned may be applied to other systems with advantage. This review will cover all the literature on reactions in which cyclodextrins bind substrates and then either catalyze their reactions or mimic a step in an enzymatic catalytic sequence. However, it will not describe work in which cyclodextrins simply change the course of a reaction without playing an obvious catalytic role involving substrate binding. For example, there are systems in which the main function of the cyclodextrin seems to be to complex a metal ion and keep it in solution.5-11 There are other studies in which binding into a cyclodextrin simply alters the selectivity of attack by an external reagent in some way12-24 or causes solubilization to facilitate phase transfer catalysis.12,25,26 Presumably such other areas are described elsewhere in this volume. While much work on artificial enzymes using cyclodextrins has been done in the author’s laboratory, and will be described, every effort is made to describe all the relevant work in the field. Several reviews of this subject already exist and should be consulted for further information.2,27-70 The readily Ronald Breslow, born in 1931 in Rahway, NJ, completed his B.A. in chemistry in1952, his M.A. in medical science in 1953, and his Ph.D. in chemistry in 1955 with R. B. Woodward, all at Harvard University. After a postdoctoral year with Alexander Todd in Cambridge, he came to Columbia University where he is now University Professor and Professor of Chemistry. His work on enzyme models, on novel conjugated aromatic and antiaromatic molecules, on electrochemical and hydrophobic methods in mechanistic chemistry, and on anticancer cytodifferentiating agents has been recognized by a number of awards, including the U.S. National Medal of Science. In 1996, he served as President of the American Chemical Society.

Biomimetic Reactions Catalyzed by Cyclodextrins and Their Derivatives.

Two-dimensionally extended, polycyclic heteroaromatic molecules (heterocyclic nanographenes) are a highly versatile class of organic materials, applicable as functional chromophores and organic semiconductors. In this Review, we discuss the rich chemistry of large heteroaromatics, focusing on their synthesis, electronic properties, and applications in materials science. This Review summarizes the historical development and current state of the art in this rapidly expanding field of research, which has become one of the key exploration areas of modern heterocyclic chemistry.

Heterocyclic Nanographenes and Other Polycyclic Heteroaromatic Compounds: Synthetic Routes, Properties, and Applications

▪ Abstract The past 10 years have witnessed a tremendous acceleration in research devoted to non-fluorinated polymer membranes, both as competitive alternatives to commercial perfluorosulfonic acid membranes operating in the same temperature range and with the objective of extending the range of operation of polymer fuel cells toward those more generally occupied by phosphoric acid fuel cells. Important requirements are adequate membrane mechanical strength at levels of functionalization (generally sulfonation) and hydration allowing high proton conductivity, and stability in the aggressive environment of a working fuel cell, in particular thermohydrolytic and chemical stability. This review provides an overview of progress made in the development of proton-conducting hydrocarbon and heterocyclic-based polymers for proton exchange and direct methanol fuel cells and describes the various approaches made to polymer modification/synthesis and salient properties of the materials formed, including those relati...

Non-Fluorinated Polymer Materials for Proton Exchange Membrane Fuel Cells

Methods for Selective Modifications of Cyclodextrins.

Polybenzoxazoles of high molecular weight were prepared easily by the solution polycondensation of 3,3′-dihydroxybenzidine dihydrochloride or 3,3′-diamino-4,4′-dihydroxybiphenyl dihydrochloride with both aromatic and aliphatic dicarboxylic acids in polyphosphoric acid. Polybenzothiazoles were prepared from 3,3′-dimercaptobenzidine dihydrochloride and dicarboxylic acids by the same procedure.



Aromatic polybenzoxazoles and polybenzothiazoles showed an excellent thermal stability up to 450°C. in air. They were insoluble in organic solvents.



Polybenzoxazole hohen Molekulargewichtes konnen leicht hergestellt werden durch Polykondensation von 3,3′-Dihydroxybenzidin-dihydrochlorid oder 3,3′-Diamino-4,4′-dihydroxybiphenyl-dihydrochlorid mit aromatischen und aliphatischen Dicarbonsauren in Polyphosphorsaure. Polybenzothiazole lassen sich nach der gleichen Methode aus 3,3′-Dimercaptobenzidin-dihydrochlorid und Dicarbonsauren herstellen.



Aromatische Polybenzoxazole und Polybenzothiazole zeigen eine ausgezeichnete thermische Stabilitat bis 450°C in Luft. Die Polymeren sind unloslich in organischen Losungsmitteln.

Polybenzoxazoles and polybenzothiazoles

Far-infrared spectra of poly-L-alanines having the α-helical conformation and the β-form structure were measured. The spectra of glycine–L-alanine copolymer, silk fibroin, and copoly-D,L-alanines with different D:L compositions were also measured. In addition to the bands so far reported, four bands at 190, 107, 120, and 90 cm−1were found for the α-helix conformation and the two bands at 442 and 247 cm−1 were found for the β form. The 442 cm−1 band consists of the parallel 432 cm−1 and perpendicular 445 cm−1 bands. The 247 cm−1 band is well defined and has strong dichroism parallel to the direction of stretching. These two bands appear also for silk fibroin and glycine–L-alanine copolymer. All the far-infrared bands of copoly-D,L-alanines can be interpreted as α-helix bands, the three peaks at 580, 478, and 420 cm−1 being ascribed to the D-residue incorporated into the right-handed α-helix or to the L-residue in the left-handed α-helix.

Keikichi Uno

Papers

Polybenzoxazoles and polybenzothiazoles

Far-infrared spectra of polyalanines with α-helical and β-form structures

Letter: The stereochemically correct catalytic site on cyclodextrin resulting in a better enzyme model.

Process for preparation of polybenzimidazoles

The Syntheses and Some Reactions of ι-Isocyanatoalkanecarboxylic Acid Chlorides and Isocyanatobenzoyl Chlorides